I live in the Santa Cruz Mountains in California. We live on a lake called Lexington Reservoir. For the past few weeks, the lake has been draining to replenish the underground aquifer. This morning, on one of my regular walks around the lake bottom, I came across this strange mass. The sack was attached to a branch submerged in the water. At first glance, I thought it was just a big piece of silicone, mostly because it looks like jelly fish that wash up on the ocean beaches. But this is a freshwater lake. I brought the thing home and sliced it open with a shovel. Inside was a clear jelly like substance with these striations. It almost seems fibrous, but in a stringy jello kind of way. There doesn't seem to be any eggs or larvae in the sack, just these fibers that cling to the tree branch it has adhered itself to. Does anyone have any idea what it could be? It is a good size sack too, as you can see from its size in comparison with the empty Coke can. Any help would be much appreciated.